1. Field of the Invention
The present invention relates generally to the fabrication of semiconductor devices, and more particularly, to a method for forming an ultra-high tensile-stressed nitride film and strained-silicon transistor devices thereof.
2. Description of the Prior Art
For decades, chip manufacturers have made metal-oxide-semiconductor (MOS) transistors faster by making them smaller. As the semiconductor processes advance to very deep sub micron era such as 65-nm node or beyond, how to increase the driving current for MOS transistors has become a critical issue.
In order to improve device performance, crystal strain technology has been developed. Crystal strain technology is becoming more and more attractive as a means for getting better performance in the field of CMOS transistor fabrication. Putting a strain on a semiconductor crystal alters the speed at which charges move through that crystal. Strain makes CMOS transistors work better by enabling electrical charges, such as electrons, to pass more easily through the silicon lattice of the gate channel.
Generally, strain in silicon can be induced in different ways: through stresses created by films in a form of poly stressor or contact etch stop layer (CESL) and structures that surround the transistor, called process-induced strain, or by employing a strained silicon wafer, where the top layer of silicon has typically been grown on top of a crystalline lattice that is larger than that of silicon. Most leading-edge chip manufacturers employ process-induced stress in some form in production today, typically tensile nitrides to improve NMOS device performance. As known in the art, tensile stress improves electron mobility and compressive stress improves hole mobility.
It is desirable to employ a nitride film having a tensile stress as high as possible in the fabrication of transistor devices. Specifically, according to the roadmap, a nitride CESL film with a tensile stress that is greater than 1.8 Gpa is required in the next-generation 45 nm process. However, so far the nitride film formed by conventional plasma-enhanced chemical vapor deposition (PECVD) methods can only reach a tensile stress of 1.2 GPa at the best.
In light of the above, there is a need in this industry to provide a method of forming nitride films having an ultra-high tensile stress for the next-generation process.